While most motorcycle manufacturers opt to house the engine and transmission together, Harley-Davidson uses a two-part engine and transmission system to power their motorcycles. The engine’s power output is transferred to the transmission through the primary chain, housed behind an oil-filled cover on the left side of the motorcycle. Just as the engine’s oil supply works to reduce internal friction, the fluid within the primary chaincase reduces wear on the chain and the transmission’s clutch plates. The primary fluid must be changed every 5,000 miles to ensure that your Harley-Davidson is ready to ride when you are.
1. Take your Softail for a brief, 10-minute ride. Shift through all five gears, six for newer Softail models, while riding at a moderate pace. Park the motorcycle on its side stand, once you return, and let it cool for 10 minutes.
2. Place an oil drain pan below the primary chaincase on the left side of the engine. Unscrew the primary drain bolt from the bottom of the primary chaincase, located directly below the round clutch inspection cover, using a 3/8-inch Allen wrench.
3. Remove the drain bolt O-ring and wipe the bolt threads and tip with a shop rag. Slip a new O-ring onto the bolt, then coat the O-ring with Harley-Davidson Formula+ Primary Chaincase Fluid. Screw the drain bolt into the primary chaincase by hand. Tighten the drain bolt to 17 foot-pounds, using a torque wrench and a 3/8-inch Allen socket.
4. Remove the round clutch inspection cover and gasket from the primary chaincase, using a T27 Torx wrench. Lift the motorcycle into an upright position and hold it in place. Fill the primary chaincase with up to one quart of Harley-Davidson Formula+ Primary Chaincase Fluid. Ideally, the fluid level should be even with the bottom of the clutch assembly, as viewed through the clutch inspection port with the motorcycle in an upright position.
5. Lower the motorcycle onto its side stand. Reinstall the clutch inspection cover and gasket onto the primary chaincase. Screw the upper bolt into place, using a T27 Torx wrench. Install the bottom-most bolt next, then alternate between bolts in a star-shaped pattern. Tighten the bolts to 10 foot-pounds, using the same method.
6. Seal your oil drain pan or pour the old oil into a container, and take it to your local Harley-Davidson repair center for recycling.